There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
The functional characteristics of purinoceptors in Chinese hamster ovary (CHO) cells
were investigated using a microphysiometer which detects small metabolic changes to
living cells in real-time as variations of pH in the extracellular microenvironment.
Uridine 5'-triphosphate (UTP) increased the extracellular acidification rate biphasically,
namely a transient and a steady response were observed. The transient phase reached
a peak (four- to fivefold the basal extracellular acidification rate in amplitude)
within 20 s and was followed by the steady phase which was sustained for more than
1 min at an amplitude less than twofold the basal extracellular acidification rate.
Both phases showed a concentration-dependent increase in response to UTP. However,
there was a significant difference in the pEC(50) value for UTP between the transient
(4.8) and steady phases (6.1). Like UTP, ATP increased the extracellular acidification
rate, but alpha,beta-methyleneATP (alpha,beta-MeATP), 2-methylthioATP (2-MeSATP),
ADP, UDP and adenosine did not. This result suggests that the acid is extruded through
a P2Y(2) or P2Y(2)-like purinoceptor. 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and
4-isopropyl-3-methylsulphonylbenzoyl-guanidine methanesulphonate (HOE642) suppressed
both phases of the UTP-stimulated extracellular acidification rate response with high
affinity (pIC(50): approximately 7.0). This result suggests that the Na(+)/H(+) exchanger
1 (NHE-1) predominantly mediates the UTP-induced acid extrusion response in CHO cells.
Elimination of extracellular Ca(2+) or treatment with thapsigargin diminished both
phases of the UTP-stimulated extracellular acidification rate. In addition, N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide
hydrochloride (W-7) also abrogated the two phases. These results are consistent with
the involvement of NHE-1 which is activated via Ca(2+)/calmodulin. Persistent exposure
to UTP reduced both extracellular acidification rate phases, causing desensitization
of the P2Y purinoceptor. This desensitization did not affect the acid extrusion response
mediated by the alpha(1)-adrenoceptor.